196 



METABOLIC HORMONES 



there are two possible sites for this action. One is the cell mem- 

 branes of the blood vessel walls and the tissues, where there is 

 evidence that insulin stimulates the transfer of glucose from the 

 blood stream to the tissue fluids. The other is the seat of chemical 

 transformation within the tissues, where intracellular enzymes, 

 particularly hexokinase, hasten the phosphorylation of glucose by 

 adenosine triphosphate (ATP). This results in the formation of 



Fig. 5-9. Changes in distribution of injected galactose caused by 

 INSULIN injection in eviscerated and nephrectomized dogs, Cams. 

 Galactose was injected at the beginning at the rate of 1 g/Kg ; ordin- 

 ates show the amounts recovered in the blood in mg per 100 g (not 

 %); abscissae show time in hours after the injection; vertical hnes 

 show the range of variation of all values in 6 or 8 specimens. 

 (a) The upper curve shows that when equilibrium is reached after 

 about 1 hour, in absence of insulin, the galactose concentration 

 is such that it occupies 45 % of the body weight, or the volume of 

 the blood only. The lower curve, for similar measurements made 

 in presence of insulin, shows that the galactose is distributed in a 

 larger volume, amounting to 70% of the body weight and equiva- 

 lent to all the body fluids, (b) A similar record in which insulin 

 is added after equilibrium in the blood has been reached in 2^ hr 

 and causes a drop to the 70 % body weight distribution, as before 

 (from Levine et al., 1950). 



glucose-6-phosphate, which is the starting-point both for utilizing 

 glucose and for converting it to glycogen (Fig. 5-8). It has recently 

 been postulated (Levine and Goldstein, 1955«) that stimulation of 

 the transfer system is the main action of insulin, and that it merely 



